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Membrane Structure
Barrier Compartmentalization
Semipermeable selectively leaky
Fluid Mosaic Model Phospholipids Proteins ~
Membrane Proteins
Channels Pumps
active transport Receptor protein sites
bind messenger molecules Transducer proteins:
2d messenger systems Structural proteins
form junctions with other neurons ~
Membrane Proteins: Ionophores
Ion Channels Non-gated
always open Gated
chemically-gated electrically-gated mechanically-gated ~
Chemically-Gated Channels
ligand-gated Ionotropic
receptor protein = channel direct control ---> fast
Metabotropic second messenger system indirect ---> slow ~
Metabolic pumps: Active Transport
Membrane proteins Pump ions
require energy Na+ - K+ Ca++ (calcium)
Also various molecules nutrients neurotransmitters ~
Biolelectric Potential
Communication within neuron electrical signal
electric current = movement of electrons
Bioelectric: movement of ions ~
Ion Distribution
Particles / molecules electrically charged
Anions negatively charged
Cations positively charged ~
Anions (-) Large intracellular proteins Chloride ions Cl-
Cations (+) Sodium Na+ Potassium K+ ~
Ion Distribution
Resting Membrane Potential
Membrane
outside
inside
Na+
Na+
Cl-
Cl-K+
K+
A-
+ + + + + + + + + + +
-----------
+ + + + + + + + + + +
-----------
more negative particles in than out Bioelectric Potential
like a battery Potential for ion movement
• current ~
Membrane is polarized
Forces That Move Ions
Concentration (C) particles in fluid move from area of
high to area of low concentration diffusion, random movement
Electrostatic (E) ions = charged particles like charges repel opposite charges attract ~
Equilibrium Potential
Also called reversal potential Distribution of single ion across
membrane e.g., EK+, ENa+, ECl-
Potential for movement of ion if channel opens units millivolts (mV) Potential outside = 0, by convention ~
Equilibrium Potential
R = gas constant F = Faraday constant T = temperature (K) Z = valence (charge) of ion ~
i
o
K K
K
ZF
RTE
][
][log
Membrane Potential
Net bioelectric potential for all ions units = millivolts (mV)
Balance of both gradients concentration & electrostatic
Vm = -65 mV given by Goldman equation ~
icliNaiK
ocloNaoK
m ClPNaPKP
ClPNaPKP
F
RTV
][][][
][][][log
Membrane Potential: Goldman Equation
P = permeability at rest: PK: PNa: PCl = 1.0 : 0.04 : 0.45
Net potential movement for all ions known Vm:Can predict direction of movement of any ion ~
Chloride ion
C
E
Cl-
Vm = -65 mV
Concentration gradient equal to electrostatic gradient.
Leaks out neuron ECl- = - 65 mV ~
K+ C
EVm = -65 mV
Potassium ion
Concentration gradient greater than electrostatic gradient.
Leaks out neuron EK = - 75 mV ~
Sodium ion
Na+
C EVm = -65 mV
Concentration gradient and electrostatic gradient into neuron.
ENa+ = +55 mV ~
Metabolic Pumps
Active Transport mechanisms Require energy
Move materials against gradient Na+ - K+ Calcium - Ca++ Nutrients, etc.~
Na+ - K+ Pump
Moves ions against gradients Pumps 3 Na+ out of cell 2 K+ into cell
Maintains gradients at rest no active role in signalling Energy = ATP ~